I'm currently trying to get a dc motor working with a specific motor controller called MC33886. My problem is figuring out how to control the speed of the motor. I saw on YouTube that 99% of motor controllers have an "enable" pin. For some odd reason, this one doesn't. If anyone can please guide me, I'd gladly appreciate the help .
I can't see any connection information in your link.
Some motor drivers expect a PWM signal on one input or on the other input depending on the direction you want the motor to move. The Pololu DRV8833 is an example.
I expect its permanently enabled. The inputs map one-to-one with the outputs so you
should be able to do most things except coasting. For each bridge you would normally PWM
one signal and hold the other low to give speed control, swap pin roles for the other direction.
The MC33886 actually has an enable and a disable pin, you could trace where they go to on
the board?
MarkT:
I expect its permanently enabled. The inputs map one-to-one with the outputs so you
should be able to do most things except coasting.
I hate it when PCBs hold the enable pin high with these sorts of h-bridge chips. There can be a huge performance difference between pulse the direction control pins and pulsing the enable pin.
I think it's safe to say pulsing the direction pins uses more power from the battery than pulsing the enable pin for the same amount to output power to the motors.
At low PWM frequencies pulsing the direction pins can sound awful as the motor brakes (and sounds like it's breaking) during each low pulse.
A disable pin is an enable pin - just with negative logic - in fact this chip has two enable
pins, one is a true enable (negative logic disable) and one a disable (negative logic enable).
MarkT:
A disable pin is an enable pin - just with negative logic - in fact this chip has two enable
pins, one is a true enable (negative logic disable) and one a disable (negative logic enable).
You are quite correct. I was in too much of a hurry with Reply #9
What I should have said is that there is no PCB holding the diasble/enable "ON".
Robin2:
What I should have said is that there is no PCB holding the diasble/enable "ON".
I don't understand what you mean.
Aren't the enable/disable pins set by the PCB?
I haven't used a DRV8833 but I'm under the impression it brakes the motor with each low pulse of the PWM signal. I don't think the DRV8833 lets the motor coast on the low pulse.
I'd be very curious to know how current consumption of the DRV8833 compares with a h-bridge which allows coasting.
I'm going to order a couple DRV8833 boards from Pololu to see how they compare with other motor drivers. I just have a hard time believing they work as well (efficiently) as h-bridges which allow coasting.
Once again, I am far behind the ball. I only looked at the datasheet for the chip - not the one for the board. Apologies to all.
I haven't used a DRV8833 but I'm under the impression it brakes the motor with each low pulse of the PWM signal. I don't think the DRV8833 lets the motor coast on the low pulse.
I haven't had the DRV8833s for long. I did not notice any strange behaviour. But I got sidetracked onto another project that needs to be able to work with 15v to 20v. Will probably get back to the 8833's in the second half of next week. I want the DRV8833s to work off a single LiPo cell.
I have been using an L298N for the higher voltage but it has no short-circuit protection and I have ordered some Toshiba TA8428K chips which should arrive Monday or Tuesday. I have no experience of them but the specs looked OK and they are cheap and need no external components.
Lets be a bit less sloppy here - some H-bridges allow coasting and some do not. It all
depends on how many of the possible states of the 4 switching devices can be commanded.
There are 9 states that don't have shoot-through, so the most complete control is only
available if all 4 switches are individually controlled. Some H-bridges do mixed-mode decay
where they control some of the combinations automatically without explicit command, so it
gets complicated.
This chip doesn't allow either output to float so you get synchronized rectification mode only,
but means you still have 4 quadrant control, at the expense of a little more dissipation due
to iron losses. For motion control this is what you need, as the response is basically linear to
the drive PWM making control loops more stable and predictable. So long as the PWM
frequency is high enough.
With floating states of the outputs the system has more complex behaviour as the voltage
across the winding isn't completely defined, merely bounded. However you can play tricks with
lower PWM frequencies and lower iron losses in the motor. Usually copper losses dominate
anyway, so the effect isn't massive.
Copper losses mean losses due to the winding resistance. Iron losses are magnetic losses
whenever the magnetic field in the laminations reverses. High PWM frequencies don't require
complete magnetic reversal, note, the inductance of the winding limits the change in current
and thus change in magnetic field, and thus iron losses are not simply proportional to frequency.
.